A common misconception is that U.S. military personnel are fit, lean, and healthy because of the military lifestyle (and its emphasis on health promotion), inferring that the military has somehow escaped the civilian obesity epidemic. To the contrary, 34% of women actively serving in the U.S. military are overweight and 6% are obese. Many women (and particularly overweight and obese women) gain weight excessively while pregnant, and excessive gestational weight gain is a significant risk factor for perinatal complications and postpartum weight retention. Postpartum weight retention, in particular, is a significant concern for women serving in the United States military, as they only 6 months postpartum to return to fitness standards and they can be discharged if they fail their fitness test. Postpartum weight retention is also a significant concern for military readiness (or the ability to quickly mobilize for national defense), which is the single most important metric for th Department of Defense. Given the negative health implications of excessive gestational weight gain and postpartum weight retention, the impediment of excess weight on military readiness and military careers, and the dearth of research on gestational weight gain and postpartum weight loss in the United States military, we propose a stepped-care gestational weight gain intervention and a stepped-care postpartum weight loss intervention for active duty women, based on the Look AHEAD Intensive Lifestyle Intervention, that accommodates the lifestyle and environment that is unique to military personnel. We will randomize 450 participants to 1 of 3 arms: a) a gestational weight gain intervention); b) a postpartum weight loss intervention, or c) a combined gestational weight gain and postpartum weight loss intervention and determine the efficacy of the interventions on gestational weight gain as well as 6-month postpartum weight loss. In addition, we will examine medical outcomes and health care utilization (from the electronic medical record) and fitness test data (from the military fitness database) by intervention arm. We will also gather process data related to treatment outcome (e.g., session participation, self-monitoring adherence, meal replacement adherence, physical activity). We will determine whether a gestational weight gain intervention, a postpartum weight loss intervention, or a combination of the two interventions is most efficacious in improving postpartum weight loss, maternal health, and military readiness. These outcomes are expected to have an important positive impact because the intervention(s) could be disseminated the entire United States Military and integrated into standard health care for pregnant/postpartum military women.